1. Field of the Invention
The invention relates to television signal processing. More particularly, the invention relates to the vertical blanking interval (VBI) portion of a television signal.
2. Description of the Related Art
A vertical blanking interval (VBI) is a portion of an analog video or television signal that is blanked, or left clear, of video or audio information to allow time for the electron gun in a television monitor's cathode ray tube (CRT) to move from the bottom to the top of the screen as it scans images. The VBI often is used to carry information other than video or audio information, such as test signals, reference signals, closed-caption signals for the hearing impaired, emergency weather information or stock market data. Also, recently, internet designers have been using the VBI to broadcast HyperText Markup Language (HTML)-formatted information, e.g., from web sites to web subscribers. The VBI typically is expressed as the number of horizontal lines scanned.
Typically, the broadcaster, such as the cable television provider, inserts or datacasts VBI data into the VBI portion of the television signal. The television signal then is transmitted to one or more video processing devices, such as signal converter or decoder (set-top) boxes, video cassette recorders (VCRs), digital video disk (DVD) recorders, or other suitable video (and audio) receivers. From the video processing devices, the television signal then is transmitted to a user system, typically a television.
Video processing devices have to pass VBI data through the device, i.e., from the device input to the device output, to make the data available to other processing devices that may be connected thereto. Not all scanned lines in the VBI contain data, thus it is inefficient for the processor in the video processing device to read all of the VBI lines to decode VBI data that may be contained only in a few of the scanned lines. Reading all of the scanned lines of the VBI can occupy valuable processing resources of the video processing device that otherwise can be used for the primary purposes of the video processing device, such as delivering audio and video services and supporting internal device programs like playback and recording functions.